Fluid sets for inkjet imaging

ABSTRACT

The present disclosure is drawn to a fluid set for inkjet imaging which includes a white inkjet ink and a fixer fluid. The white ink can include an aqueous ink vehicle, from 5 wt % to 50 wt % of a white metal oxide pigment having an average particulate size from 100 nm to 2,000 nm, and from 0.1 wt % to 4 wt % of anionic oxide particulates having an average particulate size from 1 nm to 100 nm. The white ink can also include a non-ionic or predominantly non-ionic dispersant having an acid number not higher than 100 mg KOH/g based on dry polymer weight. The fixer fluid can include an aqueous fixer vehicle and from 0.1 wt % to 25 wt % cationic polymer.

BACKGROUND

The use of ink-jet printing systems has grown dramatically in recentyears. This growth may be attributed to substantial improvements inprint resolution and overall print quality coupled with appreciablereduction in cost. Today's ink-jet printers offer acceptable printquality for many commercial, business, and household applications atlower costs than comparable products available just a few years ago.Notwithstanding their recent success, research and development effortscontinue toward improving ink-jet print quality over a wide variety ofdifferent applications.

An ink-jet image is formed when a precise pattern of dots is ejectedfrom a drop-generating device known as a “printhead” onto a printingmedium. Inks normally used in ink-jet recording are sometimes composedof water-soluble organic solvents, surfactants, and colorants in apredominantly aqueous fluid. Regarding the use of colorants, certainpigments can be more challenging than other in achieving certaindesirable properties. For example, ink opacity, durability, anduniformity can be a challenge in certain circumstances.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the disclosure will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the technology; and, wherein:

FIG. 1 depicts fluid set examples where a cationic polymer is digitallyprinted on a media substrate contemporaneously or just before printing awhite inkjet ink thereon in accordance with examples of the presentdisclosure;

FIG. 2 depicts fluid set examples where a cationic polymer is applied toa media substrate prior to (either digital or by analog application)printing a white inkjet ink thereon in accordance with examples of thepresent disclosure;

FIG. 3 depicts examples of heat fusing an image printed in as describedin FIG. 1 or 2 in accordance with examples of the present disclosure;

FIG. 4 depicts a printed article, such as that shown in FIG. 3, afterheat fusing on the media substrate;

FIG. 5 is an image of a vertical drip test conducted using a control inkand fixer; and

FIG. 6 is an image of a vertical drip test conducted using a fluid set(ink and fixer combination) prepared in accordance with examples of thepresent disclosure.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of thedisclosure is thereby intended.

DETAILED DESCRIPTION

The present disclosure is drawn to fluid sets including white ink andfixer formulations. The ink can be a water-based white inkjet ink thatcan be jetted from various types of inkjet printheads, but areparticularly friendly for use in thermal inkjet printheads. The fixerfluid can likewise be inkjettable, or can be formulated for analogapplication to a media substrate. These fluids (white ink and fixerfluid), can be printed not only on porous media, but also effectively onmore challenging non-porous polymer media, such as smooth polymersurfaces.

In accordance with this, it has been realized that inks white metaloxide pigments (e.g., zinc oxide, titanium dioxide such as rutile oranatase, zirconium oxide, etc.) can be dispersed and effectively jettedfrom thermal inkjet printheads with non-ionic or predominantly non-ionicdispersants. Unfortunately, these inks also tend to produce coating ofnon-uniform thickness when dried on non-porous substrates, whichultimately leads to poor quality prints. This problem can be solved byadding a relatively small amount (around 1-2 orders of magnitude lessthan the weight percentage of the white metal oxide pigment) of anionicoxide particulates (e.g., precipitated silica dispersion; fumed silicadispersion, anionically charged alumina-silicate particles dispersion;etc.). This, in combination with fixer applied to the media substrate totemporarily fix the ink prior to heat fusion, can provide high printquality and highly durable prints can be generated on smooth polymersubstrates. More specifically, the anionic oxide particulates of thewhite ink can act to cross-link with cationic polymer (e.g., usuallydelivered with a digitally printable or analog application fixer fluid)located at the surface of the media substrate sites. This interactiontemporarily freezes the white metal oxide pigment on the print surfaceand prevents pigment shifting and print quality degradation duringdrying. Thus, by generating a more uniform print layer (avoiding theMarangoni effect and severe coalescence), uniform and adequate inkthickness can lend itself to greater uniformity and efficient opacity ofthe printed image. Additionally, non-ionic stabilization of the whitemetal oxide pigment provides for prevention of the formation of stableaggregates (coagulation) during ink drying. Printing a relatively thickink layer on non-porous media surface in absence of strong cohesiveforces between pigment particles can lead to uncontrolled ink spreadoutside printed area boundaries and poor edge definition. This can beavoided using the inks of the present disclosure. On another note, insome examples, color gamut can be improved if this white ink is used aspart of a colored ink set, because these inks can also provide a methodof generating an on-demand white background for colored, black, oroff-white substrates.

In accordance with examples of the present disclosure, a fluid set forinkjet imaging can include a white inkjet ink and a fixer fluid. Thewhite ink can include an aqueous ink vehicle, from 5 wt % to 50 wt % ofa white metal oxide pigment having an average particulate size from 100nm to 2,000 nm, and from 0.1 wt % to 4 wt % of anionic oxideparticulates having an average particulate size from 1 nm to 100 nm. Thewhite ink can also include a non-ionic or predominantly non-ionicdispersant having an acid number not higher than 100 mg KOH/g based ondry polymer weight. The fixer fluid can include an aqueous fixervehicle, e.g., inkjettable vehicle for digital application or slurryvehicle for analog application, and from 0.1 wt % to 25 wt % cationicpolymer.

In another example, a printed article can include a non-porous polymersubstrate, and a white image printed and heat fused on the non-porouspolymer substrate. The white image can include cationic polymer, whitemetal oxide pigment having an average particulate size from 150 nm to500 nm, and anionic oxide particulates having an average particulatesize from 1 nm to 100 nm and being present at a white metal oxidepigment to anionic oxide particulates weight ratio from 5:1 to 200:1.The white image can also include non-ionic or predominantly non-ionicdispersant having an acid number not higher than 100 mg KOH/g based ondry polymer weight. The white image in this example is present on thenon-porous polymer substrate at a dry coat weight up to 50 gsm. In oneexample, the printed article can include latex particulates as part ofthe white image, e.g., glass transition temperature from 0° C. to 130°C. at a white metal oxide pigment to latex particulates weight ratiofrom 6:1 to 1:3.

In another example, a method of forming a white image, can includeapplying a fixer fluid onto a media substrate, and inkjet printing awhite ink onto the media substrate prior to, at the same time, or afterapplying the fixer fluid to the media substrate to form a white imagecomprising fixer fluid admixed with the white ink. The fixer fluid caninclude aqueous fixer vehicle and from 0.1 wt % to 25 wt % cationicpolymer. The white ink can include an aqueous ink vehicle, from 5 wt %to 50 wt % of a white metal oxide pigment having an average particulatesize from 150 nm to 500 nm, and from 0.1 wt % to 4 wt % of anionic oxideparticulates having an average particulate size from 1 nm to 100 nm. Thewhite metal oxide pigment and anionic oxide particulates can be presentin the white ink at a weight ratio from 5:1 to 200:1. The white ink canfurther include a non-ionic or predominantly non-ionic dispersant havingan acid number not higher than 100 mg KOH/g based on dry polymer weight.In this example, the cationic polymer can interact with the anionicoxide particulates to immobilize the white metal oxide pigment. Incertain specific examples, the step of heat fusing the latexparticulates of white ink after printing the white ink of the mediasubstrate to generate a heat fused image comprising the white ink can becarried out. In one example, the media substrate is a smooth polymersubstrate, i.e. non-porous. By this method, the step of applying thefixer fluid can be by inkjet application or by an analog process, e.g.,non-digital application.

In each of these examples, there are several advantages related to theinclusion of the anionic oxide particulates along with a more dominantconcentration of the white metal oxide pigment. The addition of anionicoxide particulates provides a relatively strong to very strongelectrostatic interaction with cationic polymer that may be present onthe media substrate, or as part of a fixer fluid to be printed(digitally) or otherwise applied (analog application) on a mediasubstrate. The negative charge, small size, and relative large number ofthese anionic oxide particulates provide a way of fixing relativelythick ink layer on a smooth polymer surface for drying and/or subsequentheat fusing. For example, these particulates have an opposite chargerelative to that of the cationic polymer present in a fixer coating orfixer fluid applied to the media substrate. Thus, these inks can provideelectrostatic cross-linking sites for cationic polymer molecules. Mixingof white ink containing these particulates with cationic fixer or afixer coating can very quickly create a cross-linked network, trappinglarge non-ionically-stabilized TiO₂ pigment (or other white metal oxidepigment).

FIG. 1 depicts an example where a digitally printed fixer fluid isapplied just prior to or simultaneously with a white ink in accordancewith the present disclosure. FIG. 2 depicts an example where a fixer isapplied to a media substrate prior to application of a white ink. Thefixer in this latter example can likewise be applied by digitalprinting, or alternatively, by analog application, e.g., roller, curtaincoating, blade coating, Meyer rod coating, or any other non-digitalcoating methodology suitable for producing thin layer of fixer on theprinted substrate, etc. As shown in FIGS. 1 and 2, an inkjet printingdevice 30 is adapted to digitally print a white inkjet ink 10, and insome examples, a fixer fluid 20, on a media substrate 40. The mediasubstrate can be a smooth, non-porous polymer substrate that isotherwise difficult to print on with high image quality and highdurability. Specifically, FIG. 1 shows the fixer fluid being printeddigitally from the printing device, and FIG. 2 shows the fixer fluidbeing pre-applied to the media substrate, either digitally or by ananalog coating method. In both examples, the white ink includes whitemetal oxide pigment 12, anionic oxide particulates 14, and an inkvehicle 18 which typically includes a non-ionic dispersant or dispersingagent. Water, organic solvent, and/or other ingredients can likewise bepresent in the ink vehicle. Though not required, latex particulates 16are also present in these examples, which can be used to assist with inkopacity and heat fusion of the ink to the media substrate. The fixerfluid can include cationic polymer 22 that is interactive with theanionic oxide particles of the white ink, thereby providing someimmobilization or freezing of the pigment and particles on the printmedia substrate.

In another example, as briefly mentioned, the image printed or otherwisegenerated in accordance with FIGS. 1 and 2 can be heat fused. Morespecifically, FIG. 3 shows a heat fusing device 50 which is used toapply heat 52 to the printed article to form a heat fused printedarticle as shown in FIG. 4. Because of the presence of the white metaloxide pigment 12, and in some more specific examples, the latexparticulates 16,16 b appropriately spaced, there can be enhanced lightscattering 60 and lower transmittance 62 than even more densely packedwhite metal oxide pigment, which thus provides enhanced opacity. Thisincreased opacity can be achieved by optically spacing the white metaloxide pigment from one another. For example, drying of the inks withoutlatex particulates such that all of the high refractive indexparticulates are in close contact leads to formation of a densely packedlayer of the white metal oxide pigment, which reduces their lightscattering ability and overall opacity. On the other hand, using thefusible latex particulates as shown, and typically applying heat to fusethe latex particulates, the low refractive index optical spacing canboost the opacity of the printed coating by from 0.1% to 25%, or moretypically from 5% to 20% or from 5% to 25%. In other words, the crowdingeffect of tightly-packed high refractive index (n) particulates withlittle or no voids decreases light scattering and increase transparencyof the coating. By optically spacing the white metal oxide pigment withthe low refractive index latex particulates (and typically heat fusedafter printing) an increase in opacity can be realized. That beingstated, application of thicker coatings can likewise add to opacity, andin some instances, higher opacity is not needed. Thus, the addition ofthe latex, though useful in enhancing opacity and improving heat fusion,is not required.

In accordance with this, a printed article can include up to 75, or upto 50 gsm of a total fluid (white ink+fixer) applied to a mediasubstrate. The term “up to 75 gsm” or “up to 100 gsm” is used becausetypical inkjet images include fully imaged areas as well as non-imagedand/or lower density areas. After water and solvent(s) evaporation andfusing, the gsm roughly translates into 15-50 wt % of the initial fluiddispersion flux density, i.e. thus less than 50 gsm. In one example,full density inked area may be at from 30 to 50 gsm ink/fixer film, butdensities lower in the tone ramp will be lower than this, thus the useof the phrase “up to” 75 gsm or “up to” 50 gsm. That being stated,though some areas on a media substrate might be at 0 gsm under thisdefinition (unprinted areas), there will be areas that are imaged thatrange from greater than 0 gsm up to 50 gsm (after drying or heatfusing). In a typical printed article, there is a portion of the mediathat can be printed at from 5 gsm to 50 gsm.

Turning now to the various specific ingredients that are present in thewhite ink, there can be a white metal oxide pigment. The “white” pigmentprovides much of the white coloration to the ink, though without theother ingredients in the ink, the pigment may have some transparency ortranslucency. Examples of white metal oxide pigments that can be usedinclude titanium dioxide particulates, zinc oxide particulates,zirconium oxide particulates, combinations thereof, or the like.Pigments with high light scatter capabilities, such as these, can beselected to enhance light scattering and lower transmittance, thusincreasing opacity. White metal oxide pigments can have a particulatesize from about 100 nm to about 2000 nm, and more typically, from about125 nm to 700 nm, and in still another example, from about 150 nm to 500nm. The combination of these pigments within these size ranges,appropriately spaced from one another with ingredients, good opacity canbe achieved at relatively thin thickness, e.g., 5 gsm to 50 gsm afterremoval of water and other solvent(s) from the printed ink and fixerfilm.

The white metal oxide pigment, among other solids that may be present,can be dispersed using a non-ionic dispersing agent. Suitable non-ionicdispersing agents can allow for suitable dispersibility and stability inan aqueous ink environment, while having little to no impact on theviscosity of the liquid phase of the ink as well as retaining goodprinthead reliability in thermal inkjet printheads. Dispersants meetingthese parameters are typically non-ionic or predominantly non-ionic(only weakly anionic) in character. For definitional purposes, thesedispersants are referred to as non-ionic dispersants, provided they arenon-ionic or predominantly non-ionic in nature, i.e. the acid number ofthe predominantly non-ionic/weak anionic dispersant, per dry polymer, isnot higher than 100 mg KOH/g, and is typically less than 50 mg KOH/g,most typically less than 30 mg KOH/g. That being state, in one example,non-ionic dispersing agent with no anionic properties can be used oneexample.

Examples of non-ionic dispersants that are included in this definitionare water-hydrolysable silane coupling agents (SCAs) with relativelyshort (oligomer length range of not longer than 50 units, not longerthan 30 units, or not longer than 15 units, e.g., 10 to 15 units)polyether chain(s), which are also soluble in water. An example of sucha dispersant includes Silquest® A1230 polyethylene glycol methoxysilaneavailable from Momentive Performance Materials. Other examples includesoluble low-to-midrange M (e.g., usually molecular mass of the polymerless than 15,000 Da) branched co-polymers of comb-type structures withpolyether pendant chains and acidic anchor groups attached to thebackbone, such as Disperbyk®-190 and Disperbyk®-199 available from BYKChemie, as well as Dispersogen® PCE available from Clariant.

In further detail regarding the dispersants that can be used, in oneexample, reactive hydrophilic alkoxysilane dispersants that can bepresent, and examples include, but are not limited to, hydrolysablealkoxysilanes with alkoxy group attached to water-soluble (hydrophilic)moieties, such as water-soluble polyether oligomer chains, phosphategroups, or carboxylic groups. In some examples, the dispersant used todisperse white metal oxide pigment can be a polyether alkoxysilane orpolyether phosphate dispersant. Upon dissolution in water with the whitemetal oxide pigment, the alkoxysilane group of the dispersant oftenhydrolysis resulting in formation of silanol group. The silanol group,in turn, may react or form hydrogen bonds with hydroxyl groups of metaloxide particulate surface, as well as with silanol groups of otherdispersant molecules through hydrogen bonding. These reactions lead tobonding or preferential absorption of the dispersant molecules to themetal oxide particulate surfaces and also form bonds between dispersantmolecules themselves. As a result, these interactions can form thickhydrophilic coatings of reactive dispersant molecules on surface of thewhite metal oxide pigment. This coating can increase the hydrodynamicradius of the particulates and thus reduce their effective density andsettling rate. Furthermore, the dispersant coating preventsagglomeration of the white metal oxide pigment upon settling so thatwhen sediment and settling does occur over time in the ink formulations,the settled white metal oxide pigment remain fluffy and thus are easy tore-disperse upon agitation. In still further detail, these dispersantshave a relatively short chain length and do not contribute significantlyto the ink viscosity, even with relatively high metal oxide particulateloads, e.g. over 30 wt % white metal oxide pigment in the ink.

As mentioned, a suitable alkoxysilane dispersant can have analkoxysilane group which can be easily hydrolyzed in aqueous environmentand produce a silanol group, and a hydrophilic segment. The generalstructure of the alkoxysilane group is —Si(OR)₃, where R most can bemethyl, ethyl, n-propyl, isopropyl, or even a longer (branched orunbranched) alkane chain. It is noted that the longer the hydrocarbon(R), the slower hydrolysis rate and rate of interaction with dispersedmetal oxide particulate surface. In a few highly practical examples,structures with —Si(OR)₃ where R is methyl or ethyl can typically beused. The hydrophilic segment of the alkoxysilane dispersant canlikewise be large enough (relative to the whole molecule size) in orderto enable dispersant solubility in aqueous environment, as well asprevent agglomeration of the white metal oxide pigment. In one example,the hydrophilic segment can be a polyether chain, e.g., polyethyleneglycol (PEG) or its co-polymer with polypropylene glycol (PPG).Polyether-based dispersant moieties have clean thermal decomposition,and thus, are good candidates for use. When heated above decompositiontemperature, PEG and PPG-based molecules decompose into smallermolecular fragments with high volatility or good water solubility. Thus,their decomposition usually does not form noticeable amounts of solidresidue on surface of microscopic heaters used for driving thermalinkjet printheads (which can cause thermal inkjet printheads to failover time or render them non-operational in some instances).

In further detail, examples polyether alkoxysilane dispersants that maybe used to disperse white metal oxide pigment can be represented by thefollowing general Formula (I):

wherein:

a) R¹, R² and R³ are hydroxy groups, or hydrolyzable linear or branchedalkoxy groups. For hydrolyzable alkoxy groups, such groups can have 1 to3 carbon atoms; in one aspect, such groups can be —OCH₃ and —OCH₂CH₃. Insome examples, R¹, R² and R³ are linear alkoxy groups having from 1 to 5carbon atoms. In some other examples, R¹, R² and R³ groups are —OCH₃ or—OC₂H₅.

b) PE is a polyether oligomer chain segment of the structural formula[(CH₂)_(n)—CH(R)—O]_(m), attached to Si through Si—C bond, wherein n isan integer ranging from 0 to 3, wherein m is an integer superior orequal to 2 and wherein R is H or a chain alkyl group. R can also be achain alkyl group having 1 to 3 carbon atoms, such as CH₃ or C₂H₅. Insome examples, m is an integer ranging from 3 to 30 and, in some otherexamples, m is an integer ranging from 5 to 15. The polyether chainsegment (PE) may include repeating units of polyethylene glycol (PEG)chain segment (—CH₂CH₂—O—), or polypropylene glycol (PPG) chain segment(—CH₂—CH(CH₃)—O—), or a mixture of both types. In some examples, thepolyether chain segment (PE) contains PEG units (—CH₂CH₂—O—); and

c) R⁴ is hydrogen, or a linear or a branched alkyl group. In someexamples, R⁴ is an alkyl group having from 1 to 5 carbon atoms.

Other examples of dispersants used to disperse white metal oxide pigmentcan include polyether alkoxysilane dispersants having the followinggeneral Formula (II):

wherein R′, R″ and R′ are linear or branched alkyl groups. In someexamples, R′, R″ and R′ are linear alkyl groups having from 1 to 3carbon atoms in chain length. In some examples, R′, R″ and R′″—CH₃ or—C₂H₅. R⁴ and PE are as described above for Formula (I); i.e. PE is apolyether oligomer chain segment of the structural formula:[(CH₂)_(n)—CH—R—O]_(m), wherein n is an integer ranging from 0 to 3,wherein m is an integer superior or equal to 2 and wherein R is H or achain alkyl group; and R⁴ is hydrogen, or a linear or a branched alkylgroup. In some examples, R⁴ is CH₃ or C₂H₅.

In some examples, the white metal oxide pigment present in the inkcomposition is dispersed with polyether alkoxysilanes. Examples ofsuitable polyether alkoxysilanes include (CH₃O)₃Si—(CH₂CH₂O)_(n), H;(CH₃CH₂O)₃Si—(CH₂CH₂O)_(n),H; (CH₃O)₃Si—(CH₂CH₂O)_(n), CH₃;(CH₃CH₂O)₃Si—(CH₂CH₂O)_(n), CH₃; (CH₃O)₃Si—(CH₂CH₂O)_(n), CH₂CH₃;(CH₃CH₂O)₃Si—(CH₂CH₂O)_(n), CH₂CH₃; (CH₃O)₃Si—(CH₂CH(CH₃)O)_(n), H;(CH₃CH₂O)₃Si—(CH₂CH(CH₃)O)_(n), H; (CH₃O)₃Si—(CH₂CH(CH₃)O)_(n), CH₃;(CH₃CH₂O)₃Si—(CH₂CH(CH₃)O)_(n), CH₃; wherein n′ is an integer equal to 2or greater. In some examples, n′ is an integer ranging from 2 to 30 and,in some other examples, n′ is an integer ranging from 5 to 15.

Commercial examples of the polyether alkoxysilane dispersants include,but are not limited to, the aforementioned Silquest®A-1230 manufacturedby Momentive Performance Materials, and Dynasylan® 4144 manufactured byEvonik/Degussa.

The amount of dispersant used to disperse the white metal oxide pigmentand other solids may vary from about 1% by weight to about 300% byweight of the white metal oxide pigment content. In some examples, thedispersant content range is from about 2 to about 150% by weight of thewhite metal oxide pigment content. In some other examples, thedispersant content range is from about 5 to about 100% by weight of thewhite metal oxide pigment content.

A dispersion of white metal oxide pigment suitable for forming the whiteinks of the present disclosure can be prepared via milling or dispersingmetal oxide powder in water in the presence of suitable dispersants. Forexample, the metal oxide dispersion may be prepared by millingcommercially available inorganic oxide pigment having large particulatesize (in the micron range) in the presence of the dispersants describedabove until the desired particulate size is achieved. The startingdispersion to be milled can be an aqueous dispersion with solid contentup to 65% by weight of the white metal oxide pigment or pigments. Themilling equipment that can be used may be a bead mill, which is a wetgrinding machine capable of using very fine beads having diameters ofless than 1.0 mm (and, generally, less than 0.5 mm) as the grindingmedium, for example, Ultra-Apex Bead Mills from Kotobuki Industries Co.Ltd. The milling duration, rotor speed, and/or temperature may beadjusted to achieve the dispersion particulate size desired.

The anionic oxide particulates that are also included in the white inkcan be any of a variety of anionic oxide particles, such as anionicsemi-metal oxide particles, e.g., anionic silica and/or aluminaparticulates. One example is an anionically-stabilized colloidal silicadispersion. Other examples include precipitated silica dispersions,anionically charged alumina silicate particle dispersion,anionically-stabilized fumed silica dispersions (such as Cab-O-Sperse®silica series available from Cabot Corporation). Typically, in manycolloidal silica dispersions, particulates have a strong anionic(negative) charge at about pH >7, and thus, can instantly or veryquickly react with cationic polymer applied as part of the fixer fluidto a media substrate, forming a loose cross-linked network. Generally,the higher is the number of particulates per volume of the ink, thestronger is their cross-linking/pigment immobilization effect uponmixing with the fixer layer or fluid on the media substrate. Thus, insome examples, there are advantages for using small anionically chargedsilica, e.g., the same weight percentage of anionic oxide particulatesin an ink formulation at 3 nm would have roughly 10³ times moreparticulates than a dispersion having 30 nm particulates. Thus, the useof small particles, e.g., from 1 nm to 100 nm, or more typically from 1nm to 50 nm, relative to the size of the white metal oxide pigments,e.g., 100 nm to 2000 nm, can provide some advantage with respect tofixing an ink with a fixer coating or composition.

Anionic oxide particulates, such as anionic colloidal silica indispersion form, are commercially available, and examples includeSnowtex® Colloidal Silicas available from Nissan Chemical Corporation,e.g., Snowtex® ST-S (spherical particulates; median particulate size˜2-3 nm); Snowtex® ST-30LH (spherical particulates; median particulatesize ˜30 nm); and Snowtex® ST-UP (elongated particulates (particulatedimensions ˜9-15/40-100 nm). Other anionic oxide particulates includeIDISIL® colloidal silica available from Evonik Industries (particulatesize 5-50 nm); Ludox® colloidal silicas available from W.R. Grace & Co.such as Ludox® HS-30 (particulate size ˜12 nm); Ludox AM, Ludox® SM-AS,Ludox® AS-30, Ludox® AS-40 (particulate size ˜12 nm), etc.; Bindzil® andLevasil® grades of colloidal silica available from Akzo Nobel N.V.

It is also notable that in certain instances, there can be furtherimprovements when adding latex particulates to the inks of the presentdisclosure. For example, by combining white metal oxide pigment withlatex particulates, opacity can be increased if increased opacity isdesired for a given application, even though latex does not have a highrefractive index. In one aspect, if latex is added, a white metal oxidepigment to latex particulate weight ratio can be from 6:1 to 1:3. Incertain specific examples, by selecting white metal oxide pigment with ahigh refractive index (e.g. from 1.8 to 2.8), and latex particulateswith a relatively lower refractive index (e.g., from 1.3 to 1.6), theopacity of the ink when printed on a media sheet can be unexpectedlyincreased compared to an ink without the added latex particulates (evenwhen the latex is replaced with an equivalent concentration of whitemetal oxide pigment).

In further detail, in providing some optical spacing between white metaloxide pigment particles by interposing latex particulates there between,opacity can be increased compared to inks without the latex particulatespresent. In other words, a layer of more densely packed high refractiveindex white metal oxide pigment can actually be less opaque (to light)than a layer of less densely packed white metal oxide pigment (e.g.,pigment crowding effect). It may be considered counterintuitive becauseone expects better light scattering capability and opacity of coatinghaving a higher concentration of high refractive index white metal oxidepigment. Thus, in certain examples, by decreasing the density of thewhite metal oxide pigment or pigment content, and replacing the pigmentwith essentially colorless latex particulates, such as fusible latexparticulates, opacity could actually be increased.

As mentioned, the particulate size of the white metal oxide pigment canbe from 100 nm to 2,000 nm, but in other examples, the particulate sizecan be from 125 nm to 700 nm, or from 150 nm to 500 nm. These largersized particulates are considered to be efficient particulate sizes forlight scattering when spaced appropriately by the latex particulates.The more efficient the light scattering, typically, the more opaque theprinted ink layer may be. Thus, the white inks of the present disclosurecan be formulated such that when printed, the latex particulates providean average space between white metal oxide pigment ranging from 20 nm to2000 nm, in one example. In other examples, the average space betweenwhite metal oxide pigment (as provided primarily by the latexparticulates) can be 50 nm to 500 nm, from 150 to 300, or in onespecific example, about 220 nm to 250 nm. Alternatively, if latex is notadded, opacity can be increased by increasing the thickness of theprinted layer of white ink. Other techniques of increasing white opacitycan also be used.

In further detail when using latex, optical spacing can beexperimentally determined by printing the ink on a media substrate,fusing the ink by applying heat at a temperature about 2° C. to 110° C.above the minimum film formation temperature of the latex particulates,and evaluating using Transition Electron Microscopy (TEM) cross-sectionphoto of a printed white ink layer after drying. If the opacity providedby the white ink is not high enough, the ratio of white metal oxidepigment to latex particulates can be adjusted up or down, as effective,or the thickness of the ink can be increased. That being stated, anadvantage of the white inks of the present disclosure is that in someinstances, thickness does not need to be increased to increase opacity.For example, by appropriately spacing the white metal oxide pigment withthe latex particulates, opacity can be boosted from 0.1% to 25%, andmore typically, from 5% to 25%.

In addition to assisting with enhanced opacity, as briefly mentioned,the latex particulate, if included, can also provide enhanceddurability. More specifically, the use of latex particulates, includingfusible latex particulates that are thermally or otherwise cured afterprinting on the media substrate, can provide added durability to theprinted image. Thus, in some examples, the latex can provide the dualrole of enhancing opacity by appropriately spacing the white metal oxidepigment, and can also provide durability on the printed media sheet.This is particularly the case in examples where there may be high metaloxide particulate loads that are dispersed by appropriate dispersingagents. Films formed by hard ceramic particulates (such as highrefractive index metal oxides on surface of low porosity and non-porousmedia substrates tend to have very poor mechanical properties. Thefilm-forming behavior of latex particulates described herein can bindthe relatively large white metal oxide pigment (with dispersing agentpresent in the ink) into continuous coating that can be very durable.Additionally, as mentioned, the low refractive index of the polymer filmcreates low refractive index or “n” domains, i.e. optical spacersbetween high n white metal oxide pigment, thereby simultaneouslyenhancing opacity of the print.

Coalescence of latex particulates into continuous phase creates lowrefractive index domains in the coating. The refractive index of thefused latex in the coating may range from 1.3 to 1.6, and in oneexample, can be from 1.4 to 1.6, or 1.4 to 1.5. The white metal oxidepigment can have a refractive index ranging from 1.8 to 2.8, or from 2.2to 2.8. Specific examples include zinc oxide (about 2.4), titaniumdioxide (about 2.5 to 2.7), zirconium oxide (about 2.4), etc. Typically,the difference in the refractive indexes can be from about 0.2 to 1.5,or more, if possible (typically, the higher is the better), though thisis not required as long as there is enough of a difference that theopacity can be increased at least to some degree by the optical spacingand the refractive index difference.

Conditions enabling usage of the polymer latex in the white inkformulations of the present disclosure are dependent on what type of inkis being prepared. For example, for thermal inkjet printingapplications, the glass transition temperature of the latex particulatesmay range from 0° C. to 130° C., or from 40° C. to 130° C. in someexamples.

The monomers used in the latexes can be vinyl monomers. In one example,the monomers can be one or more of vinyl monomers (such as vinylchloride, vinylidene chloride, etc.), vinyl ester monomers, acrylatemonomers, methacrylate monomers, styrene monomers, ethylene, maleateesters, fumarate esters, itaconate esters, or mixtures thereof. In oneaspect, the monomers can include acrylates, methacrylates, styrenes, ormixtures thereof. The monomers can likewise include hydrophilic monomersincluding acid monomers, and hydrophobic monomers. Furthermore, monomersthat can be polymerized in forming the latexes include, withoutlimitation, styrene, α-methyl styrene, p-methyl styrene, methylmethacrylate, hexyl acrylate, hexyl methacrylate, butyl acrylate, butylmethacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate,propyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate,octadecyl acrylate, octadecyl methacrylate, stearyl methacrylate,vinylbenzyl chloride, isobornyl acrylate, tetrahydrofurfuryl acrylate,2-phenoxyethyl methacrylate, benzyl methacrylate, benzyl acrylate,ethoxylated nonyl phenol methacrylate, isobornyl methacrylate,cyclohexyl methacrylate, tri methyl cyclohexyl methacrylate, t-butylmethacrylate, n-octyl methacrylate, lauryl methacrylate, trydecylmethacrylate, alkoxylated tetrahydrofurfuryl acrylate, isodecylacrylate, isobornylmethacrylate, isobornyl acrylate, dimethyl maleate,dioctyl maleate, acetoacetoxyethyl methacrylate, diacetone acrylamide,N-vinyl imidazole, N-vinylcarbazole, N-Vinyl-caprolactam, combinationsthereof, derivatives thereof, or mixtures thereof.

Acidic monomers that can be polymerized in forming latexes include,without limitation, acrylic acid, methacrylic acid, ethacrylic acid,dimethylacrylic acid, maleic anhydride, maleic acid, vinylsulfonate,cyanoacrylic acid, vinylacetic acid, allylacetic acid, ethylidineaceticacid, propylidineacetic acid, crotonoic acid, fumaric acid, itaconicacid, sorbic acid, angelic acid, cinnamic acid, styrylacrylic acid,citraconic acid, glutaconic acid, aconitic acid, phenylacrylic acid,acryloxypropionic acid, aconitic acid, phenylacrylic acid,acryloxypropionic acid, vinylbenzoic acid, N-vinylsuccinamidic acid,mesaconic acid, methacroylalanine, acryloylhydroxyglycine, sulfoethylmethacrylic acid, sulfopropyl acrylic acid, styrene sulfonic acid,sulfoethylacrylic acid, 2-methacryloyloxymethane-1-sulfonic acid,3-methacryoyloxypropane-1-sulfonic acid, 3-(vinyloxy)propane-1-sulfonicacid, ethylenesulfonic acid, vinyl sulfuric acid, 4-vinylphenyl sulfuricacid, ethylene phosphonic acid, vinyl phosphoric acid, vinyl benzoicacid, 2-acrylamido-2-methyl-1-propanesulfonic acid, combinationsthereof, derivatives thereof, or mixtures thereof.

Regarding the latex particulates, the latexes can have various shapes,sizes, and molecular weights. In one example, polymer in the latexparticulates may have a weight average molecular weight (M_(w)) of about5,000 M_(w) to about 500,000 M_(w). In one aspect, the latexparticulates can have a weight average molecular weight (M_(w)) rangingfrom about 100,000 M_(w) to about 500,000 M_(w). In some other examples,the latex resin has a weight average molecular weight of about 150,000M_(w) to 300,000 M_(w).

Further, the average particulate diameter of the latex particulates canbe from about 10 nm to about 1 μm; in some other examples, from about 10nm to about 500 nm; and, in yet other examples, from about 50 nm toabout 300 nm. The particulate size distribution of the latex is notparticularly limited, and either latex having a broad particulate sizedistribution or latex having a mono-dispersed particulate sizedistribution may be used. It is also possible to use two or more kindsof latex particulates each having a mono-dispersed particulate sizedistribution in combination.

The white inks described herein are very useful for thermal inkjetapplication. In one example, a reactive hydrophilic alkoxysilanedispersant can be used to assist in particulate dispersion andjettability. In some specific examples, inkjet printing of whitecoatings or patterns with adequate opacity (>50-60%) can benefit from arelatively high pigment load (e.g. white metal oxide pigment above 2 wt%, above 5 wt %, above 8 wt %, etc.). Jetting of high pigment load(particularly with other solids) inks becomes challenging even for piezoprintheads. However, with the use of an appropriate dispersant, such asthe non-ionic or predominantly non-ionic dispersants described herein,more reliable performance of higher metal oxide particulate loadsprinted from thermal inkjet printheads with low nominal drop weight (aslow as 10 ng, or even as low as 5 ng) can be realized.

The white inks of the present disclosure also include an aqueous inkvehicle. As used herein, “ink vehicle” refers to the liquid fluid inwhich the white metal oxide pigment and the latex particulate aredispersed to form an ink. Ink vehicles are known in the art, and a widevariety of ink vehicles may be used with the systems and methods of thepresent technology. Such ink vehicles may include a mixture of a varietyof different agents, including, surfactants, solvents, co-solvents,anti-kogation agents, buffers, biocides, sequestering agents, viscositymodifiers, surface-active agents, water, etc. Though not part of theliquid vehicle per se, in addition to the colorants, the liquid vehiclecan carry other solid additives as well, such as polymers, UV curablematerials, plasticizers, etc. Additionally, the term “aqueous inkvehicle” refers to a liquid vehicle including water as a solvent. In oneaspect, water can include a majority of the liquid vehicle.

Turning now to the fixer fluid, cationic polymer can be added to variousink or liquid vehicles to form fixer fluids of various viscosities forvarious application processes. Cationic polymers that may be used caninclude guanidinium or fully quaternized ammonium functionalities, suchas quaternized polyamine copolymers. In one example, the cationicpolymer might not contain primary or secondary ammonium functionalities,such as polyallylamine or polyethylene imine. Generally, for somedigital application processes, i.e. thermal inkjet application, theweight average molecular weight (M_(w)) of the cationic polymer allowsviscosity of 1 cP to 25 cP at 25° C., 1 cP to 15 cP at 25° C., or 1 cPto 10 cP at 25° C., as measured on a Brookfield viscometer. Thoughviscosity outside of this range can be used, particularly for piezoinkjet applications or for analog (non-digital printing) applications,e.g., 1 cP to 35 cP at 25° C. (for piezo inkjet) and 1 cP to 500 cP at25° C. for analog applications. Typical weight average molecular weightfor the cationic polymer can be less than 500,000 M_(w), and in oneaspect, less than 50,000 M_(w). In another example, cationic polymerscan have high charge densities to improve fixing efficiencies. As such,cationic charge densities can be higher than 1000 microequivalents pergram cationic functionality. In one aspect, higher than 4000microequivalents per gram can be used. Additionally, concentrations canbe low to avoid regulatory issues with aquatic toxicity, e.g., from 0.1wt % to 25 wt %, and in one aspect, 1 wt % to 5 wt %, or in anotheraspect, from 1 wt % to 2.5 wt %.

In additional detail, classes of cationic polymers that can be usedinclude, but are not limited to, quaternized polyamines, dicyandiamidepolycations, diallyldimethyl ammonium chloride copolymers, quaternizeddimethylaminoethyl(meth)acrylate polymers, quaternized vinylimidizolpolymers, alkyl guanidine polymers, alkoxylated polyethylene imines, andmixtures thereof. It is to be understood that one or more polycationsmay be used, and that any desirable combination of the polycations canbe used. One or more ions of the cationic polyelectrolytes may beion-exchanged for a nitrate, acetate, mesylate, or other ion. As anon-limiting example, one preferred material is Floquat® FL2350, aquaternized polyamine derived from epichlorohydrin and dimethyl amine,commercially available from SNF Inc.

Typical ink vehicle or fixer vehicle formulations described herein caninclude water and other ingredients, depending on the application methoddesired for use. For example, when jetting the ink or fixer, theformulation may include co-solvents present in total at from 0.1 wt % to40 wt %, though amounts outside of this range can also be used. Further,surfactants can be present, ranging from 0.01 wt % to 10 wt %. Thebalance of the formulation can further include or other vehiclecomponents known in the art, such as biocides, viscosity modifiers,materials for pH adjustment, sequestering agents, preservatives, and thelike. Typically, the ink vehicle can include water as one of a majorsolvent and can be referred to as an aqueous liquid vehicle. It is notedthat the fixer fluid may be formulated for inkjet application or foranalog coating processes, and thus, the ingredients and concentrationsfor such different applications can vary widely. For example, a thickerslurry may be used for analog application, or a less viscous fluid maybe used for digital application.

Classes of co-solvents that can be used can include organic co-solventsincluding aliphatic alcohols, aromatic alcohols, diols, glycol ethers,polyglycol ethers, 2-pyrrolidinones, caprolactams, formamides,acetamides, and long chain alcohols. Examples of such compounds includeprimary aliphatic alcohols, secondary aliphatic alcohols, 1,2-alcohols,1,3-alcohols, 1,5-alcohols, ethylene glycol alkyl ethers, propyleneglycol alkyl ethers, higher homologs (C₆-C₁₂) of polyethylene glycolalkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, bothsubstituted and unsubstituted formamides, both substituted andunsubstituted acetamides, and the like.

Consistent with the formulation of this disclosure, various otheradditives may be employed to enhance the properties of the inkcomposition for specific applications. Examples of these additives arethose added to inhibit the growth of harmful microorganisms. Theseadditives may be biocides, fungicides, and other microbial agents, whichare routinely used in ink formulations. Examples of suitable microbialagents include, but are not limited to, NUOSEPT® (Nudex, Inc.),UCARCIDE™ (Union carbide Corp.), VANCIDE® (R.T. Vanderbilt Co.), PROXEL®(ICI America), and combinations thereof.

Sequestering agents, such as EDTA (ethylene diamine tetra acetic acid),may be included to eliminate the deleterious effects of heavy metalimpurities, and buffer solutions may be used to control the pH of theink. From 0.01 wt % to 2 wt %, for example, can be used. Viscositymodifiers and buffers may also be present, as well as other additivesknown to those skilled in the art to modify properties of the ink asdesired. Such additives can be present at from 0.01 wt % to 20 wt %.

It is noted that when discussing the present fluid sets, printedarticles, and/or methods, each of these discussions can be consideredapplicable to each of these embodiments, whether or not they areexplicitly discussed in the context of that embodiment. Thus, forexample, in discussing refractive index related to a composition or theopacity in the context of the printed article, such elements are alsorelevant to and directly supported in the context of the methods orfluid sets described herein, and vice versa.

It is to be understood that this disclosure is not limited to theparticular process steps and materials disclosed herein because suchprocess steps and materials may vary somewhat. It is also to beunderstood that the terminology used herein is used for the purpose ofdescribing particular examples only. The terms are not intended to belimiting because the scope of the present disclosure is intended to belimited only by the appended claims and equivalents thereof.

It is be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Furthermore, it is understood that any reference to open endedtransition phrases such “comprising” or “including” directly supportsthe use of other know, less open ended, transition phrases such as“consisting of” or “consisting essentially of” and vice versa.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 to about 5” should beinterpreted to include not only the explicitly recited values of about 1to about 5, but also include individual values and sub-ranges within theindicated range. Thus, included in this numerical range are individualvalues such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4,and from 3-5, etc. Additionally, a numerical range with a lower end of“0” can include a sub-range using “0.1” as the lower end point.

EXAMPLES

The following illustrates some examples of the disclosed inks, printedarticles, and methods that are presently known. However, it is to beunderstood that the following are only exemplary or illustrative of theapplication of the principles of the present disclosure. Numerousmodifications and alternative examples may be devised by those skilledin the art without departing from the spirit and scope of the presentcompositions and methods. Thus, while the present inks and methods havebeen described above with particularity, the following examples providefurther detail in connection with what are presently deemed to be theacceptable embodiments.

Example 1—White Pigment Dispersion

A white pigment dispersion was prepared by milling TiO₂ pigment powder(Ti-Pure® R960 available from DuPont) in a water-based slurry containing˜50.8 wt % of the dry pigment powder. Disperbyk®-190 non-ionic/weaklyanionic (acid number-10 mg KOH/g) branched polymer X (available from BYKChemie) was used as dispersant at 1.5 wt % per dry pigment weight. Themilling was done in MiniCer® bead mill available from NETZSCH PremierTechnologies, LLC., utilizing YTZ milling beads with 0.3 mm diameter.Mean particulate size of the TiO₂ in the milled dispersion was about 260nm (as determined by NANOTRACK® particulate size analyzer fromMicrotrack Corp., Montgomeryville, Pa.

Example 2—White Ink Formulations

Two white ink formulations were prepared, one with anionic oxideparticulates as well as a control without anionic oxide particulates, asshown in Table 1 below:

TABLE 1 Control Ink Ink 1 Components (wt %) (wt %)2-methyl-1,3-propanediol 9 9 2-Pyrrolidinone 16 16 ₁Tergitol ® 15-S-7(90 wt % actives) 1 1 ₂Capstone ® FS-35 (25.3 wt % actives) 1.98 1.98₁Tergitol ® TMN-6 (90 wt % actives) 1 1 Acrylic binder latex (41.4 wt %actives) 21.74 21.74 Anionic Colloidal Silica (₄Snotex ® ST-S) — 0.97(31.05 wt % actives) ₂Ti-Pure ® R960 TiO₂ (50.8 wt % actives) 29.5329.53% dispersed with ₃Disperbyk ®-190 (at 1.5 wt % based on theTiO₂content) - As Prepared in Example 1 Water Balance to Balance to 100 wt %100 wt % ₁Available from the Dow Chemical Company; ₂Available fromDuPont; ₃Available from BYK Chemie; and ₄Available from Nissan Chemical.

Example 2—Comparative Printing

Control Ink and Ink 1 were both printed from HP 792 printhead with HPOfficeJet® 8000 printer. A cationic fixer including about 2.5 wt % of aFloquat® FL2350 cationic polymer (available from SNF Inc.) dissolvedaqueous formulation also containing ˜20 wt % of 2-pyrrolidone was jettedtogether with the white inks (similar to that shown in FIG. 1) from aseparate printhead (HP 940). More specifically, a pattern of 9rectangular shapes was printed with each ink and fixer combination. Theprint media used was signage black vinyl (“Milano” brand). Ink coveragedensity in the prints was about 50 gsm for white inks while fixing fluidcoverage density was varying (left to right) from 0 wt % to 32 wt % (inincreasing increments of 4 wt %) based on the white coverage gsmdensity. After printing, the media samples were positioned verticallyfor 5 minutes to allow the loose or non-fixed pigment to flow down theprint surface. The prints were then manually dried and cured by heat gunat temperature ˜100-120° C. for 3 minutes. The results of the test areshown in FIGS. 5 and 6. FIG. 5 is an image of the printed rectangles andassociated ink flow from each rectangle for the Control Ink, and FIG. 6is an image of the printed rectangles and associated ink flow from eachrectangle for Ink 1. As can be seen, the impact of the anionic colloidalsilica particulates with respect to the cationic fixer and associatedreactivity of inks with non-ionically dispersed TiO₂ pigment exhibitedno vertical running over the entire range from 8 wt % to 32 wt % ofcationic fixer fluid flux density. Conversely, only a narrow window of 8wt % to 16 wt % of cationic fixer fluid flux density exhibited novertical running for the Control ink. In other words, the Control Inkwithout the added anionic oxide particulates had poorer fixing fluidreactivity compared to Ink 1. As DB190 used to prepare the white metaloxide pigment dispersion is a polymeric non-ionic dispersant with alittle anionic functionality, the TiO₂ pigment dispersed at 1.5 wt % ofDB190 can only be immobilized within a narrow fixer/ink ratio window(˜8-16 wt %). Outside of this fixer/ink window, the ink dripped down themedia surface (see FIG. 5). The ink with 0.3 wt % addition of theSnowtex® ST-S silica was gelled on the spot at much wider fixer/inkratio (8-32 wt %, see FIG. 6). This shows that by adding even a verysmall amount of anionically charged oxide particulates to non-ionicwhite ink formulation, dramatic improvement in fixing robustness can beachieved.

While the disclosure has been described with reference to certainembodiments, those skilled in the art will appreciate that variousmodifications, changes, omissions, and substitutions can be made withoutdeparting from the spirit of the disclosure. It is intended, therefore,that the present disclosure be limited only by the scope of thefollowing claims.

What is claimed is:
 1. A fluid set for inkjet imaging, comprising: awhite inkjet ink, comprising: an aqueous ink vehicle, from 5 wt % to 50wt % of a white metal oxide pigment having an average particulate sizefrom 100 nm to 2,000 nm, from 0.1 wt % to 4 wt % of anionic oxideparticulates having an average particulate size from 1 nm to 100 nm, anda non-ionic or predominantly non-ionic dispersant having an acid numbernot higher than 100 mg KOH/g based on dry polymer weight; and a fixerfluid, comprising: aqueous fixer vehicle, and from 0.1 wt % to 25 wt %cationic polymer.
 2. The fluid set of claim 1, wherein the white metaloxide pigment and anionic oxide particulates are present in the whiteink at a weight ratio from 5:1 to 200:1, wherein the white metal oxidepigment has an average particulate size from 150 nm to 500 nm, andwherein the anionic oxide particulates have an average particle sizefrom 1 nm to 50 nm.
 3. The fluid set of claim 1, wherein the white metaloxide pigment includes titanium dioxide particulates, zinc oxideparticulates, zirconium oxide particulates, or combinations thereof. 4.The fluid set of claim 1, wherein the anionic oxide particulates includeanionically-stabilized colloidal silica dispersion,anionically-stabilized fumed silica dispersion, precipitated silicadispersion, fumed silica dispersion, or anionically chargedalumina-silicate particle dispersion.
 5. The fluid set of claim 1,further comprising from 2 wt % to 30 wt % of latex particulates having aglass transition temperature from 0° C. to 130° C., and wherein thewhite metal oxide pigment and latex particulates are present in thewhite ink at a weight ratio from 6:1 to 1:3.
 6. The fluid set of claim1, wherein the non-ionic or predominantly non-ionic dispersant is ahydrophilic alkoxysilane dispersing agent, a water-hydrolysable silanecoupling agents with oligomer length range polyether chains, or alow-to-midrange branched co-polymer of comb-type structure withpolyether pendant chains and acidic anchor groups attached to itsbackbone.
 7. The fluid set of claim 1, wherein the fixer fluid isformulated for inkjet application having a viscosity less than about 35cP at 25° C.
 8. The fluid set of claim 1, wherein the fixer fluid isformulated for analog application having a viscosity from 1 cP to 500 cPat 25° C.
 9. A printed article, comprising: a non-porous polymersubstrate; and a white image printed and heat fused on the non-porouspolymer substrate, the white image comprising cationic polymer, whitemetal oxide pigment having an average particulate size from 150 nm to500 nm, anionic oxide particulates having an average particulate sizefrom 1 nm to 100 nm and being present at a white metal oxide pigment toanionic oxide particulates weight ratio from 5:1 to 200:1, and non-ionicor predominantly non-ionic dispersant having an acid number not higherthan 100 mg KOH/g based on dry polymer weight, the white image beingpresent on the non-porous polymer substrate at a dry coat weight up to50 gsm.
 10. The printed article of claim 9, further comprising latexparticulates having a glass transition temperature from 0° C. to 130°C., wherein the white metal oxide pigment and latex particulates arepresent at a weight ratio from 6:1 to 1:3.
 11. A method of forming awhite image, comprising: applying a fixer fluid onto a media substrate,the fixer fluid comprising aqueous fixer vehicle, and from 0.1 wt % to25 wt % cationic polymer; and inkjet printing a white ink onto the mediasubstrate prior to, at the same time, or after applying the fixer fluidto the media substrate to form a white image comprising fixer fluidadmixed with the white ink, the white ink, comprising: an aqueous inkvehicle, from 5 wt % to 50 wt % of a white metal oxide pigment having anaverage particulate size from 150 nm to 500 nm, from 0.1 wt % to 4 wt %of anionic oxide particulates having an average particulate size from 1nm to 100 nm, wherein the white metal oxide pigment and anionic oxideparticulates are present in the white ink at a weight ratio from 5:1 to200:1, and a non-ionic or predominantly non-ionic dispersant having anacid number not higher than 100 mg KOH/g based on dry polymer weight,wherein the cationic polymer interacts with the anionic oxideparticulates to immobilize the white metal oxide pigment.
 12. The methodof claim 11, further comprising the step of heat fusing the latexparticulates of white ink after printing the white ink of the mediasubstrate to generate a heat fused image comprising the white ink. 13.The method of claim 11, wherein the media substrate is a smooth polymersubstrate.
 14. The method of claim 11, wherein the step of applying thefixer fluid is by inkjet application.
 15. The method of claim 11,wherein the step of applying the fixer fluid is by analog, non-digitalapplication.